Telephone transmission circuit



June 22, 1937'.

S. B. WRIGHT TELEPHONE TRANSMISSION CIRCUIT Filed July 6, 1936 2 Sheets-Sheet 1 5.1). VIZ/157M INVENTOR Dllsabler Opposing Suppresszr ATTORNEY June 22 1937.

S. B. WRIGHT TELEPHONE TRANSMISSION C IRCUIT Filed July e, 1936. ZSheets-Sheet 2 EN Q N INVEN'IIOR BY 5.3. W M

ATTORNEY Patented June 22, 1937 STAT TELEPHONE rRANsinssIoN omoorr Sumner Bisbee Wright,

South Orange, N. J., as-

signer to American Telephone and Telegraph Company, a corporation of New York Application July 6, 1936, Serial No. 89,213

19 Claims.

This invention relates to telephone transmission circuits, and more particularly to a circuit in which a plurality of telephone links equipped with echo suppressors or related devices are to be connected in tandem. One of the links may be a radio or a cable link such as is, or may be, used for transatlantic communication and which will be supplied with devices called vodases, for certain purposes to be explained hereafter.

The object of the invention is to limit the lockout to a minimum when a plurality of links including the radio or cable link is connected, and more particularly to provide an arrangement for connecting such a radio or cable link to long distance wire circuits in such a Way that the echo suppressors on the wire circuits do not increase the lockout interval or zone'beyond the value obtained on a call over the cable circuit alone.

In the circuit involving my invention use is made of a system of transmitting terminal echo suppressors located only at important switching points, such as regional centers, as described in my copending application Serial No. 748,765, filed October 17, 1934. As described in that application, the echo suppressors are disabled except when more than one link are involved in a connection. The act of connecting together two or more links automatically places the echo suppressors in connection at the regional centers.

The broad scheme of connections for long distance telephonic purposes on circuits in such a country as the United States is described in an article on General Switching Plan for Telephone Toll Service,.by Osborne, published in the Bell System Technical Journal, July, 1930. In my copending application and in the article mentioned, reference is made to RC-RC links extending between a few important switching 4 points in this country, the terminations of these links being at so-called regional centers. Reference is also made to PO-RC links which fan out from regional centers to other slightly less important switching points, called primary outlets or toll centers. Both of these links are normally operated on a four-wire basis and may be connected at the switching point on either a two wire or a four-wire basis. In addition, consideration is to be given to another type of link, such as that illustrated by the present trans- Atlantic radio link, or by a correspondingllong cable, permanently connected. to'a portion of four-wire circuit. This latter type-is subject to much greater operating difliculties and, consequently, it is the usual practice to have the channel of such a link in one direction normally disabled through one or more devices called a vodas, this term being an abbreviation for voice-operated device anti-singing. It is well illustrated in patent to Crisson Vet al., No. 1,837,316, December 22, 1931." I

The present application is a continuation in part of. my copending application, Serial No.

748,766, filed October 17, 1934.

The invention will be better understood by reference to the following specification and the accompanying drawings in which Figures 1, 2 and 3 are conventionalized representations of the three types of links mentioned above; Fig. 4 shows the connection of an RC-RC link with a' vodas link; Fig. 5 shows the circuit of Fig. 4 extended by connection to a PORC link; Fig. 6 shows some of the details by which the purpose of the invention is carried out, and Fig. 7 shows furtherdetails by which the purpose of the invention is carried out.

The first two types of links, as shown diagrammatically in Figs. 1 and'2, are equipped with echo suppressors which are normally disconnected but which may be connected into circuit for the pur pose and in the manner described in my c'opend ing application, Serial No. 743,765. In thatapplication, also, a description is given of a new typeof suppressor, which I call the transmitting suppressor in that a suppressor is operated by speech when the speech first arrives on the link and is about to be transmitted over the link. The link of Fig. 2 may beused without connection to other RC-R,C links or PO-R.C links, and in that case, according to the invention of said copending application, the suppressors will not in general be connected. This is feasible either because the RC-RC link may be relatively short, or because it isa high speed line, such as an unloaded cable circuit. In the event, 2 however, of the connection of such links, arrangement is made for the introduction orco'nnection of the transmitting terminal suppressors at the regional centers, this being accomplished through relays operated on the introduction of the cord circuit connecting the two links, and the connection of two such links does not permit opportunity for lockout. If, however, more than two links are connected, then a certain amount of lockout will occur over one or more of i the RC-''RC links. 7 i 1 a It is the purpose of this invention toprovide arrangements by which when-connection is made to a vodas link, the echo suppressors on'the RC-RC links are prevented from being 'connected, thisiforthe purpose/of preventing the i 4 The arrangement shown in Fig;

' increase off lockout zonedue to such 'an RC-'-R.C link. Ifaccomplish this by having a tone signal sent from station A to the other re 1 5 fgional center whenever the specialcable or ra-,

, dio Connection is put up. IThis tone'operat'es a disabling circuit to disable the remote suppressor. 1 At thecompletion of the call another tonersignal is sent out to place the suppressor mi commission for other calls that may go through thedistant regional center.- a

these circumstances, itris seen that there is no increase in thelockout zone over that which is a present inthe cable-or'radio Portion of the vodas' link. Fig. 5'showsthe extensionof the circuit of 'Fig. 4*t'o include a P0'R.C link, and with the I normal cord circuit; arrangement described in my" copending application, Serial No. 748,765," the terminals'u'ppress'ors at switching point B would be introduced both on the RCRQ terminal and'the 3Q PORC terminal. f This would increase the lock out zoneto the extent 'of including the RC-'RC link which might be as much as severalthousand miles long. 'To' prevent thisQI provide,'ac cording to this invention, means associated with the cord B, the details for this being shown inFigs. 6 and j .7, in which Li, and Lz'are the opposite sides of a "repeatered four-wire circuit.

7 is fundament'ally, the same as that shown in Fig-'6, the

cut-off relay-CO being shown and the suppressor andnormal toll line cireuit'being shown'rnorein detail. ,,The suppressor and normal toll line oire5 *cuit is substantially-the same as that; shown in Fig. 11. of my copending application; Serial No. 748,765., The details-"of the invention will-be described in connection with Fig. 7. ,flIhe terminal of the R. CRC link which is to beconnected to For, simplicityi; the terminal suppressor which would be at the 4 end of this link is here shownv offset in parallel jbelow the cut-off [relay CO 55 which is operated by battery 16 over the'sleeve of the lower jackofthelterrninal so as to disconnect the normal'toll Iineeircuit' and echo suppressor at station .A wheneverjthe vodas link is connected;

Upon connection, however, of thePORC link at station B,either on a four-wire or a two-wire basis, the suppressor on the RC'RC link at the stationB wojuld,be connectedintocircuit through the co d c ircuit connection atfth'at stationoper- V fating'on therelayl5, This is a connection which was is required in the event: that the lac-ac link at its-right end were to be connected to another RCR C or RC,PO link, but it is desired to dis- .able. this suppressor in the event that switching islmade tothe vodas link. To thisendthere are 7.9 installedat the stationA two generators F1 and Eziofffrequency f1" and f2,'OI1e-Of which-may, at

the appropriate timebe connected'to send a spurt ofalternating currentgover-the transmissionline toiapparatuswhich willdijsaLble the suppressor 'contactatfl, thus disabling the suppressor. V V e j operation of the relay l8 will also close the circuit 7 I circuit at regional center'A which will disable the a 7 suppressor on'the RC- RC, link at regional center the vodas link is-sho-wn at the upper right-hand part of thefigure as terminating atistation A;

on a four-wirebasis if desired.

t. th o h r end. p ith linkfaaii g 92 t S 7 a spurt of different frequency toput the suppresof the cord circuit ,H 'at' station A-to relays l8 and IS in parallel; The relay I9 is a' reasonably fast-operating relay and, when operated, will at ,sor back in commission under control of relay l5; 7 .Battery 16 is connected through the upper'sleeve contact22 connect thegeneratorF1 of frequency 1; across the transmission line. -Alternating current of this frequency will then be transmitted until the-circuit for th is generator is broken" at thepoint 2I' by the relay- .l8-,which is a slowoperate relay. This spurt of current, which is selected at station Biby theffllter passing frequency f1, will thenoperate the polar relay 23 i through the I amplifier detector ADa to open the The for the slow-release relay 26,which would operate a and would place the generator F2 of frequency '1;

across the line' except for the fact that its circuit is broken at on the operation of relay l9. 7

Upon disconnecting the cord circuit |l;relay l9 quickly releases, thus openlngthe {circuit of] gen- .erator F1 at a second point and closing at 20 the" circuitfor generator, F2 of frequency 1: untilthe relay.26 releases, Thecorrespondingspurt of the transmission line is transmitted through filter of frequency f2 and iamplifieredetector AD; to w again operate the polar relay 23,.whi ch, in this CiiSByOlOSGSthG contact-at '24 thus returning the echo suppressor to the circuitiat station B. T

In case the cord circuit connection at A is from the RCRC link to another RC- -RC link or to an RC-PO link, the circuit containing-thegenera if;

alternating currentoffrequency f2 passingover tors F1 and F2 is not brought intooperatioml This maybe accomplished simply by providing another ncord circuit with battery 16 connected only to thelower sleeve thereof or by using a battery of different potential in theother cord circuit and making relays l8, [Band 26 marginal j j sothat they will not operate on this new potential. ;On the other hand,these, results may be" accomplished as shown in the lower right-hand portion of Fig. 7,; where'a terminal for the] 'RCRC link appropriatelfo'r connection to ane other RC'.RC link, an RCe-PO link; oria sub scriber circuit is shown connected 'in parallel through the c ontacts jof cut-off relay CO to the terminal already described. If cordcircuit ll is a not connected, cut-01f relay CO will not be oper; V ated and the lower terminal which includes the 3 echo suppressoryis available to 'cord circuit 3|.

In this arrangement, which is described in copending application, Serial No. 748,765, the'fourwire link is brought to a two-wire basis through the hybrid set 36, and the echosuppressor. is made available but is normallyjdisconn'ected at'the f oute'rcontacts of relay" 34.- On setting up cord circuit 3| for connection'to RCRC or RC-PO- link 46, battery 33 acts through the sleeve on-j, nection to introduce the echo suppressor. When a connection is made to subscriber circuit 42,

battery 44' operates relay 38 ,to prevent the intro 'duction of. theecho suppressor. Also, as disclosed in said 'copending applicatiomthe lower terminal may be connected to the RCRC or RC- -PO link From the' above, it fisseen thatthrough thisinvention I have providedi means" whereby when an Rc- RC'link is connected to another RC'RC f V or an RC"P.O. l ink, the terminal suppressors are i e connected as described in my copending applica,'-"

tion', Serial No. 748,765, butmeans also whereby- 7 if the connection is to a'linkfcontaining vodases,

'the near terminal suppressor of the RC-RC link is left disconnected and the terminal suppressor at the remote end which would normally be put into action on the extension of the circuit into an RC-PO link is disabled by the act of putting up a cord circuit at the point where the RC-RC link is connected to the vodas link. Furthermore, when this cord circuit is taken down, the terminal suppressor at the remote end is automatically enabled. Incidentally, it should be noted that the putting up of the cord circuit at B connects in the terminal suppressor at the regional center end of the PORC link. This is not only permissible but desirable to prevent echo return from the PO end of the link and its introduction does not add to the lockout for the reason that it is not operated by speech traveling in the direction toward the vodas link.

In this specification, frequent reference has been made to four-wire circuits. This is a convenient term to use but it is to be understood that so far as this invention is concerned, it may mean either two pairs of physical wires or it may means a single pair of wires using two separate channels, one in one direction and the other in the other direction.

What is claimed is:

1. In a communication system comprising several links, one link being a normally disabled link containing a vodas, two or more links being adapted to be connected in series, the method of limiting lockout to a portion of the vodas link which consists in supplying terminal transmitting echo suppressors to one end of PO-RC links and each end of RCRC links to be connected, leaving these normally disconnected, connecting these at switching points when connection of links including the vodas link is made, and disabling the suppressors on the RCRC links when switching connection is made to the vodas link.

2. In a communication system comprising several links, one link being a normally disabled link containing a vodas and a portion of which is a two-way one channel transmission path, the method of limiting lockout to the two-way one channel portion which consists in supplying ter-- minal transmitting echo suppressors to one end of the PORC links and each end of the RCRC links to be connected, leaving these normally disconnected, connecting these at switching points when connection of links involving the two-way one channel portion is made and disabling the suppressors on the RC-RC links when switching connection is made to the vodas link.

3. In a communication system comprising several RCRC links and one link containing a vodas, two or more of these links being adapted to be connected in series, the method of limiting lockout to the vodas link which consists in supplying terminal transmitting echo suppressors to each end of the RC-RC links to be connected, leaving these normally disconnected, connecting these at the switching points when connection of links including the vodas link is made, and leaving the near suppressor in the link which is adjacent the vodas link disabled and disabling the more remote suppressor in that link.

4. In a system comprising several four-wire links and an intermediate two-wire link and a vodas portion adjacent each end of the two-wire link, the remaining four-wire links being equipped with single terminal echo suppressors, means for limiting lockout to the two-wire link when several links are connected in series, comprising means for normally leaving the suppressors disc'o'nncted' an'd 'for connecting them as transmit- 'ting suppressors at any switching point on connection of two links at that point, and means from the vodas link.

6. In a system comprising several links operating on a two-channel basis and an intermediate two-way single channel portion, and a vodas portion adjacent each end of the single channel portion and constituting a vodas link, the

remaining two channel links being equipped with single terminal echo suppressors, means for limiting lockout to the single channel portion when several links are connected in series, comprising means for normally leaving the suppressors disconnected and for connecting them as transmitting suppressors at any switching point on connection of two links at that point, and means for leaving that suppressor adjacent that link with vodases disabled when connection to that link is made. I

7. In a system comprising several links operating on a two-channel basis and an intermediate two-way single channel portion, and a vodas portion adjacent each end of the single channel portion and constituting a vodas link, the remaining two channel links being equipped with single terminal echo suppressors, means for limiting lockout to the single channel portion when several links are connected in series, comprising means for normally leaving the suppressors disconnected and for connecting them as transmitting suppressors at any switching point on connection of two links at that point, means for leaving that suppressor adjacent that link with vodases disabled when connection to that link is made, and further means for disconnecting transmitting echo suppressors more remote from the vodas link.

8. The combination of claim 7 characterized by the fact that the remote suppressors are disconnected by electric impulses transmitted from a point adjacent the vodas terminal.

9. The combination of claim 7. characterized by the fact that the suppressor adjacent the link with vodases is enabled by a circuit connection through the sleeve of the switching connection at that point and that the remote suppressors are disconnected by a tone transmitted from the vodas switching point.

10. In a communication system, a plurality of four-wire links and a two-wire link adapted to be connected in series with one or more of the four-wire links at one end, means for preventing echoes comprising echo suppressors supplied to each four-wire link, the suppressors being normally disconnected, means for connecting in the suppressors at a switching point and maintaining such connection if the circuit does not include the two-wire link, and further means for disconnecting the suppressors in the four-wire links when the two wire link is included in the circuit.

11. The combination of claim 10 characterized by the fact that the suppressors in the four-wire links are restored to connection when the two- Wire link is removed.

12. In a communication system including a four-wire link to be connected in series with other links and supplied with echo suppressors normally ldisconnected, 'means connecting, echo suppressors when thelinkis connected to other linksof the same character, means for disablingv the suppressor, at the remote end of this link when connections are-made atthe near end to a'link of a difierentcharacter, and further means for enabling the suppressor at the; remotezend when that connection at the near end is'brok'en.

am a communication systemlcomprising .a fourewire link with terminals at stationsA and B remote from each'other, the link being adapted for extension-by connection to'other links at the two stations, echo suppressors supplied to r the j 1 link and means at B responsive to incoming sigails. from A to' disable the echo suppressor at B atthe beginning of a connection established at A iand respcnsive to incoming signals at the ter' .mination of the connection at A to again restore the connection of the eoho supp'ressor.

14.111 a communication system, a plurality of four-wire links and a two-wire link adapted to be connected in series with the four-wire links ,at one end, means forpreventing echoes com prising echo suppressors supplied to the four-wire links, the suppressors being normally disconnected, means for connecting the suppressors atra f switching point and maintainingsuch connection if the circuit does not include the two-wire link, and further means for disconnecting the connected suppressors in one of the four-wire links when the two-wire link is included in the-circuit -l5'.' In a communication system including a, plurality of iour wire links and a two-wire link, means'at a switching point for establishing series connections betweensaid four-wire links and between one of said four-wirelinks and said two'- wire link, normally disconnected echo suppressors for each four wire link, means-for connecting in the suppressors at the switching point and for 'maintaining such connection when a series connection is established between said four-wire links, and means, when a series connection is established between one of said four-wire links and said two-wire link, for preventing the connection of suppressors in thefour-wire link and for dis connecting any such suppressorwhich isalready connectedi 16 In a communication system includingja vodas link, a subscriber link and a-plurality of four-wire links, means at a switching point, for

establishing series connections between said four- 1 wire links, between one. of said four-wire links which is connected, andfmeans for preventing 1 the connection of the suppressor in the four-wire link at the'switching point when a series conwire links and saidsubscriber link.

nection is established between'one of said four r 17. In a communication system, including a four-wire link with terminals at stations A and B remote from each other, the link being adapted for extension by connection to other links at the two stations, echo suppressors supplied to the;link

and means at B responsive to the establishment V of a connection with saidlink at A Ior disabling the echo suppressor at B and responsive to the" disestablishment of the connection at A to again restore the connection of the echo suppressor;

l8. In a communication system, a four -wire link provided at stationjA with a plurality of'terminals for connection withvone or more other links thereat on a two-wire basis and with tone or more other links thereat on a four-wire basis,

station A for disconnecting any of said terminals used for connection with other links on a twowire basiswhen the link is connected with .an-

other link on a four-wire basis, andrneans at station E responsive to incoming signalsfrom station A to disable the echo suppressor-at sta,

tion B at the beginning of a connection established at station A and responsive to incoming signals at the termination of the connection at A to again restore the connection of the echo suppressor.

station, a vodas link, a subscriber link and a plurality of four-wire links terminating thereat, one of said four-wire links being provided at said station with a plurality of terminals for conneotion of said link with said vodas link on a wire links on, a twowire basis,means at'said station operative'when said link is connected to any other link on, a four-wire basis for. discon-V terminating at stations'A and B remote from each 7 other and adapted; forextension by connection to other'links at the two stations, the link being echo suppressors-s pp ied to thelink, means at rfour-wireibasis and for connection of saidlink with said subscriber link or with the other fournecting' any of said terminals used for connection with other links on'a two-wire basis, normally disconnected echo suppressors for the four-wire links, means for connecting the echo suppressors at the switching station and maintaining them connected when said four-wire link isconnected with any of the other four-wire Iinkameans, whensaid four-wire linkis connected'with said vodas link, for preventing the connection of suppressors'in .said.four-wire link and an discon V necting any such suppressoriwhich is connected, V i

and means for preventing'the connection of the suppressor in said four-wire link atothe switching 'statiorrwhen said link is connected "with said subscriber link.

6O V-SUMVNER Bfsnnn WRIGHT;

, 7 a i 35 19. In a communication system, a switching 

